The present invention relates broadly to a phase shifter apparatus, and in particular to a .pi.-section digital phase apparatus.
In modern high frequency radar and communication systems, the antenna pattern must be moved at very rapid rates. This scanning is normally achieved in array antennas through the use of a matrix of small radiator elements whose radiation phases are systematically and electronically varied. The necessary phase gradients across the antenna are usually generated in discrete steps by a plurality of such electronic phase shifter elements.
In the prior art, a major handicap in the past phase shifter elements has been in the inability to exactly reproduce the diodes upon which the characteristics of the diode phase shifter elements are significantly dependent. However, this problem has been essentially resolved by semiconductor manufacturers, so that phase shifter development attention is directed to the improvement of the phase shifter elements themselves. The design of the present phase shifter element permits is beneficially to be physically smaller than the conventional elements of the loaded transmission line type.
In the military market, there is an increasing demand to fabricate monolithic digital phase shifters at extra high frequencies (EHF) with low insertion loss. However, as the frequency increases, the insertion loss requirements become very difficult to meet. Recent advances in the art have produced a 4-Bit monolithic digital phase shifter, which incorporates conventional circuit configurations, but only achieved only about 5 dB insertion loss at 10 GH which is excessively large for most military applications. Clearly there is a need for new techniques or configurations to design digital monolithic phase shifters with low insertion loss at high frequencies (X-Band and above). In the present invention, a .pi.-section digital phase shifter apparatus which is suitable for extra high frequency (EHF) applications, offers low insertion loss and excellent phase tracking capability, is presented.
The present .pi.-section digital phase shifter apparatus is also suitable for monolithic implementation and as such will have low cost so that it may be used in large military antenna arrays. Since the .pi.-section digital phase shifter apparatus has all the outstanding merits of the conventional .pi.-section design but with a different distribution of the elements and values, it will therefore, find wide practical application in the system design where conventional and even .pi.-section designs are not feasable to use from technical and economical stands.